[security] Upgrade playwright to the latest version (#1161)

- I've locally verified that it doesn't break anything.

[docs.homepage] Minor style fixes

[docs] Adds documentation for OAuth (#1059)

[tls] Allow setting min and max TLS version (#968)

[config] Provide a way to access config file directory in configs. (#911

)

- Add `{{ configDir }}` macro that expands to the config file directory.
- This will be useful to specify file paths relative to the config file
  directory, e.g. oauth json config, certificates, script, etc.

[probes.dns] Don't reset latency on each run (#834)

[common.file] Fix accessing files from Google Storage (#783)

#396 broke accessing Google Storage as path.join converts any double slash into a single slash.

[probes.external] Fix serverutils. (#748)

We should not be writing to buffered stdout and stderr. This change
was introduced recently in v0.13.4:
  github.com//pull/695

[surfacers.prometheus] Allow configuring metrics prefix through a fla…

…g. (#732)

- Add a new flag `--prometheus_metrics_prefix` to set metrics prefix for
 the prometheus surfacer.

- In a typical multi-tenant deployment, one would want to set metrics
prefix for all tenants. Since configs are usually tenant specific,
configs are not a good place for that, while binary flags are usually
controlled by the operator, making them a good place for such settings.

Fix client cert handling when cert reloading is enabled (#697)

Since cloudprober is the client, the dynamic cert loading needs to be
implemented in GetClientCertificate rather than GetCertificate.